1. Field of the Invention
The present invention relates to improvements in the field of light weaponry, and directed more particularly to improvements in the barreling for 30 or 50 caliber rapid fire weapons having an interchangeable barrel, and requiring a low flash profile.
2. Description of the Related Art
The relevant art of interest describes various embodiments of the M2 class machine gun, typically used against infantry, unarmored or lightly armored vehicles, planes or boats, light fortifications and the like.
Since their invention by John Browning machine guns have operated principally as follows:                The gunner pulling the bolt assembly/bolt carrier rearward by way of the cocking lever to the point bolt carrier which engages a sear and stays in this rear position until trigger is activated        The trigger is activated making the bolt carrier move forward which                    Loads a fresh round into chamber and locking bolt            And causing firing of the round by way of a firing pin or striker hitting the primer that ignites the powder when bolt reaches locked position,                        The recoil unlocking and removing the spent case from the chamber and ejecting it out of the weapon as the bolt is moving rearward        A recoil spring loading the next round into the firing chamber.        Usually the recoil spring aka main spring tension pushes bolt back into battery and a cam strips the new round from a feeding device, belt or box.This cycle is repeated as long as the trigger is activated by the gunner. Releasing the trigger resets the trigger mechanism by engaging a sear so the weapon stops firing with bolt carrier fully at the rear.        
The rate of firing of the weapon is largely a function of Newton's second law with the inertia of the recoil being largely a function of the weight of the barrel. Therefore in general, the lighter the barrel, the faster the recoil, and the higher number of rounds per minute can be fired.
The M2 has varying cyclic rates of fire, depending upon the model. For example the M2HB (heavy barrel) air-cooled ground gun having an approximately 85 lb barrel has a cyclic rate of 450-575 rounds per minute. The AN/M2 aircraft gun having a barrel weighing approximately 24 lbs has a cyclic rate of 750-850 rpm; this increases to 1,200 rpm or more for AN/M3 aircraft guns fitted with electric or mechanical feed boost mechanisms. These maximum rates of fire are generally not achieved in use, as sustained fire at that rate will wear out the bore within a few thousand rounds, necessitating replacement. The M2HB's sustained rate of fire is considered to be anything less than 400 rounds per minute.
Typically the M2 is mounted on a turret attached to a vehicle or an aircraft. The M2 can be water cooled, typically during ground applications, but many times when mounted in aircraft or light vehicles, water cooling can be cumbersome. This was compensated in air cooled versions by adding a heavy barrel which could weigh up to 85 lbs but is done to allow a larger surface area to increase heat dissipation. When extreme heating is caused during heavy use the barrels wear significantly and would need to be changed out more frequently, with a long procedure involving several individuals to get the weapon back into operation.
Therefore it is advantageous to have a light barrel with improved heat transfer characteristics.
A later version known as the Quick Change Barrel (QCB) was developed with a barrel weighing approximately 11-14 Kg, or 24-30 lbs. The QCB was designed to be removed from the front of the weapon having the barrel screwed or otherwise mounted to the internals of the weapon, including but not limited to, a barrel extension, buffer, and bolt. This was done by the gunner advancing to the front of the weapon releasing a lock, and unscrewing the barrel from the front of the weapon by hand or by use of some form of ratcheting tool. Some current applications of the M2 having the QCB are not suited for the barrel to be removed from the front of the weapon. One example being an M2 mounted to a HMVV with little room to maneuver to retract the weapon into the vehicle to gain a frontal approach to the barrel, causing exposure to the gunner should an attempt be made to change the barrel from outside the vehicle.
Therefore the QCB gave the advantage of taking less time and manpower to change the barrel but did so at the cost of exposing one to potential enemy fire.
Therefore it would be advantageous during such times to extract the barrel through the rear of the receiver (body) of the weapon, without necessitating an involved process and having sufficient maneuvering room to complete the barrel change in tight quarters.
Because the M2 was intentionally designed to be fit into many configurations, it can be adapted to feed from the left or right side of the weapon by exchanging the belt-holding pawls, the belt feed pawl, and the front and rear cartridge stops, then reversing the bolt switch. The conversion can be completed in under a minute with no tools. Therefore one skilled in the art will recognize various configurations for the present inventions depending upon the needs and requirements of the user.